Processes for treating halogen-containing gases

ABSTRACT

There are disclosed various processes, apparatuses and systems for treating a halogen-containing gas such as F 2  that involve generating a plasma in order to reduce chemically the halogen-containing gas into products that are more environmentally manageable. According to a particular embodiment, a reducing agent is mixed with the halogen-containing gas to produce a feed gas mixture and a non-thermal plasma is generated in the feed gas mixture in the presence of liquid water. According to another embodiment, a vaporized portion of a liquid reducing agent is mixed with the halogen-containing gas to produce a reaction mixture and a non-thermal plasma is generated in the reaction gas mixture to reduce the halogen-containing gas.

PRIORITY CLAIM

This application is a continuation-in-part of pending U.S. applicationSer. No. 09/905,654, which has been assigned a filing date of Jul. 11,2001 now U.S. Pat. No. 6,962,679.

FIELD OF THE DISCLOSURE

The present disclosure relates to processes and apparatuses for treatinghalogen-containing gas, particularly fluorine gas.

BACKGROUND

Halogen-containing gases are environmental hazards and must be removedor reduced from emission sources. Treatment of fluorine gas (F₂) isespecially problematic since it is only marginally soluble in water and,thus, cannot be efficiently removed from an effluent stream via waterscrubbing. The solubility in water is also poor for otherhalogen-containing gases such as trichloroethylene, chloroform,perchloroethylene, various chlorofluorocarbons (“CFCs”), and variousperfluorinated carbons (“PFCs”). Effluent streams from semiconductormanufacturing often contain such halogen-containing gases. F₂ is ofparticular interest since it is becoming more common as an emissionproduct from NF₃-based dielectric chamber cleaning processes.

Conventional treatment of F₂ gas involves combustion with a fuel gas(e.g., natural gas or butane) at 700-800° C. in a bum box resulting inthe formation primarily of hydrogen fluoride (HF), carbon dioxide (CO₂)and water. In addition to the high heat requirements and the need for afuel gas, the conventional treatment method suffers from corrosionproblems since the formed HF is highly corrosive at such hightemperatures.

An alternative thermal process for destroying F₂ involves reacting theF₂ gas with steam in the presence of an oxidation source (e.g., air)(see Flippo et al., “Abatement of Fluorine Emissions Utilizing an ATMICDO™ Model 863 with Steam Injection”(http://www.semiconductorsafety.org/meetings/proc2001/20.pdf)).According to this article, the steam acts as a reducing agent forreducing the F₂ gas into HF.

Treatment of various halogen-containing gases other than F₂ via plasmareactions have also been disclosed. For example, U.S. Pat. No. 5,187,344describes decomposing CFCs or trichloroethylene by reacting the CFC ortrichloroethylene with water in the presence of a thermal plasma. U.S.Pat. No. 6,187,072 B1 describes oxidizing PFCs under plasma conditionsto produce F₂. Grothaus et al., “Harmful Compounds Yield to NonthermalPlasma Reactor”, Technology Today, (pub. Southwest Research InstituteSpring 1996) describes treating NF₃ by adding H₂ gas and passing theresulting mixture through a pulsed corona non-thermal plasma reactor.The products were said to be F₂ and HF.

So-called “point-of-use” plasma abatement of PFCs in semiconductorprocessing effluent streams has also been described (see, e.g.,Vartanian et al., “Plasma Abatement Reduces PFC Emission”, SemiconductorInternational, June 2000, (hereinafter “Vartanian”) and “Evaluation of aLitmas “Blue” Point-of-use (POU) Plasma Abatement Device forPerfluorocompound (PFC) Destruction”, International SEMATECH, TechnologyTransfer #98123605A-ENG (1998) (hereinafter “SEMATECH disclosure”).Point-of-use abatement involves placing a high-density plasma source(n_(e)>10¹²/cm³) in the foreline of a process tool between theturbomolecular and dry pumps. Both Vartanian and the SEMATECH disclosuremention that H₂ could be an additive gas in the plasma.

Despite these efforts, a need continues to exist for efficient methodsand apparatuses for treating halogen-containing effluent gases thatoperate at low temperature and atmospheric pressure. Such a needparticularly exists for halogen-containing gases that are onlymarginally soluble in water such as F₂.

SUMMARY OF THE DISCLOSURE

Halogen-containing gases are commonly-occurring emissions frommanufacturing or cleaning processes such as etching in semiconductormanufacturing or metal cleaning in automobile manufacturing.Fluorine-laden gases are also a major byproduct from aluminum smelting.The disclosed processes and apparatuses offer an efficient abatementoption for substantially decreasing or eliminating the amount ofhalogen-containing gas released into the atmosphere by industry.

In particular, there are disclosed various processes for treating ahalogen-containing gas such as F₂ that involve generating a plasma inorder to chemically reduce the halogen-containing gas into products thatare more environmentally manageable.

A first embodiment involves providing a treatment gas that includes atleast one halogen-containing gas, mixing at least one gaseous reducingagent with the treatment gas resulting in a feed gas mixture, andgenerating a non-thermal plasma in the feed gas mixture in the presenceof a liquid to reduce the halogen-containing gas. The non-thermal plasmamay be a silent discharge plasma according to one variant of the firstembodiment.

A second embodiment involves providing a treatment gas that includes atleast one halogen-containing gas, mixing at least one gaseous reducingagent with the treatment gas resulting in a feed gas mixture, andgenerating a plasma in the feed gas mixture in the presence of liquidwater to reduce the halogen-containing gas.

A third embodiment involves introducing a halogen-containing gas and agaseous reducing agent into a chamber, introducing a liquid into thechamber, generating a non-thermal plasma in the chamber to reduce thehalogen-containing gas, and exhausting the resulting reduction productfrom the chamber. According to one variant of the third embodiment, thechamber contains at least one electrode and the liquid flows as a filmover at least a portion of the electrode.

A fourth embodiment involves providing a chamber defining at least onegas inlet for receiving a feed gas mixture that includes ahalogen-containing gas and a gaseous reducing agent, and at least onewater inlet for receiving liquid water; providing at least one firstelectrode disposed within the chamber; providing at least one secondelectrode disposed within the chamber; flowing the liquid water over atleast a portion of the first electrode; and applying electric potentialto the first and second electrodes so as to generate a plasma in thefeed gas mixture and reduce the halogen-containing gas. According to onevariant of the fourth embodiment, the first electrode defines at leastone second gas inlet for introducing the gaseous reducing agent throughthe liquid water and into the chamber so as to mix with thehalogen-containing gas and form a feed gas mixture.

There is also disclosed a further embodiment for treating fluorine gasthat contemplates providing a treatment gas that includes fluorine gas,mixing at least one reducing agent with the treatment gas resulting in afeed gas mixture, and generating a non-thermal plasma in the feed gasmixture to convert the fluorine gas to hydrogen fluoride gas.

Water-soluble gaseous reduction products resulting from these disclosedprocesses can be dissolved in water for further treatment or recyclingrather than discharged into the atmosphere. For example, F₂ gas is onlymarginally soluble in water. In contrast, the HF gas produced byreduction of F₂ gas is water-soluble and is easily removable from a gasstream via scrubbing.

The liquid present during generation of the plasma can serve a number ofpurposes. First, it absorbs a significant amount of the heat generatedby the exothermic reduction reaction. Accordingly, the operating bulkgas temperatures during the plasma generation do not exceed about 100°C. in many variants of the disclosed processes. Thus, the corrosiveeffect of the gas phase reduction products is substantially diminishedcompared to the corrosive effect at the 700 to 800° C. operatingtemperatures of the conventional combustion process. Second, if theliquid is water, the water-soluble gaseous reduction products candissolve in the water that is present in the plasma reactor. Thus,scrubbing of the reduction product stream can be substantiallycompleted, or at least initiated, in the plasma reactor. Third, theliquid can be the source of the reducing agent that reacts with thehalogen-containing gas. For example, the liquid may be vaporized toproduce a gaseous reducing agent that can be mixed with the treatmentgas as described above.

One embodiment of a process for treating a halogen-containing gasutilizing a liquid reducing agent involves introducing ahalogen-containing gas and a liquid reducing agent into a chamber. Aportion of the liquid reducing agent is vaporized in the chamber and anon-thermal plasma is generated in the chamber to reduce thehalogen-containing gas.

Also disclosed is a novel plasma reactor apparatus that includes achamber defining at least one first gas inlet for receiving a first gas,and at least one water inlet for receiving liquid water; at least onefirst electrode disposed within the chamber and defining a first surfacethat is in fluid communication with the water inlet for receiving liquidwater, and at least one second gas inlet for receiving a second gas; andat least one second electrode disposed within the chamber and opposingthe first surface of the first electrode; wherein a dielectric barrieris disposed on the first surface of the first electrode and/or a surfaceof the second electrode. Another embodiment of a novel plasma reactorapparatus includes a chamber; means for generating a non-thermal plasmain the chamber that includes at least one electrode; means forintroducing a liquid over at least a portion of the electrode; and meansfor bubbling or introducing a first gas through the liquid and into thechamber for reaction in the non-thermal plasma.

A further disclosure concerns a system for treating a halogen-containinggas that includes a plasma reactor for reducing halogen-containing gas,a halogen-containing gas source in fluid communication with the plasmareactor, a reducing agent source in fluid communication with the plasmareactor, and a liquid source in fluid communication with the plasmareactor.

The foregoing features and advantages will become more apparent from thefollowing detailed description of several embodiments that proceeds withreference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments are described below with reference to the followingfigures:

FIG. 1 is a sectional view of one embodiment of a novel non-thermal,film discharge plasma reactor for use in the disclosed processes;

FIG. 2 is a sectional view of a first embodiment of a novel electrodearrangement in a non-thermal, film discharge plasma reactor for use inthe disclosed processes;

FIG. 3 is a sectional view of a second embodiment of a novel electrodearrangement in a non-thermal, film discharge plasma reactor for use inthe disclosed processes;

FIG. 4 is a sectional view of one embodiment of a non-thermal plasmareactor for use in the disclosed processes;

FIG. 5 is a schematic of one embodiment of a system that includes thedisclosed process;

FIG. 6 is a graph depicting the amount of remaining F₂ vs. appliedplasma energy according to examples of one embodiment of the disclosedprocess;

FIG. 7 is a graph depicting the amount of remaining F₂ vs. appliedplasma energy according to additional examples of one embodiment of thedisclosed process; and

FIG. 8 is a sectional side view of a further embodiment of a plasmareactor for use in the disclosed processes.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

The following definitions are provided for ease of understanding and toguide those of ordinary skill in the art in the practice of theembodiments.

“Ambient pressure and temperature” mean pressures and temperatures thattypically exist in an environment without any external controls orenergy such as a vacuum or heating. Typically, ambient pressure isapproximately atmospheric pressure and ambient temperature isapproximately room temperature (i.e., about 20 to about 30° C.).

“Non-thermal plasma” denotes a plasma having species and electrons atvery different temperatures. In contrast, a “thermal plasma” denotes aplasma whose species and electrons are at about the same temperature.

“Treatment gas” encompasses any gas or gas mixture that includes atleast one constituent that can be destroyed or converted to a moreenvironmentally manageable species via the disclosed processes orapparatuses.

Halogen-containing gases that may be treated with the disclosedprocesses and apparatuses include fluorine gas (F₂) andfluorine-containing gases (e.g., PFC, and fluorides such as NF₃, C₂F₆,CF₄, SiF₄ and SF₆), chlorine-containing gases (e.g., Cl₂,trichloroethylene, chloroform, SiCl₄, SiCl₂H₂, and perchloroethylene),fluorochloro-containing gases (e.g., CFCs), bromine-containing gases(e.g., Br₂ and brominated hydrocarbons), and iodine-containing gases(e.g., iodated hydrocarbons). The disclosed processes and apparatusesare particularly suitable as a viable alternative to water scrubbing forgases that are only marginally soluble in water such as F₂,trichloroethylene, chloroform, perchloroethylene, various CFCs andvarious PFCs.

The treatment gas may include a mixture of different halogen-containinggases and, optionally, non-halogenated gases such as nitrogen (N₂) andinert gases that do not act as significant reducing or oxidizing agents(e.g., Ar). Oxygen is another optional component of the treatment gas.The amount of halogen-containing gas in the treatment gas mixture mayvary, for example, from about 0.000001 volume % to about 25 volume %.

The reducing agent may be any material capable of donating hydrogen oran electron to the halogen-containing gas to effectuate reduction of thehalogen-containing gas. Illustrative reducing agents include H₂,hydrocarbons, ammonia, hydrazines, hydrides (e.g., B₂H₆ and LiAlH₄),amines (e.g., ethylamine and butylamine), amides (e.g., urea andacetamide), water and similar hydrogen-rich materials. Mixtures of suchreducing agents could also be employed. An inert gas may also be mixedwith the reducing agent gas. The reducing agent should be in the form ofa gas when it is mixed with the treatment gas. However, a liquidreducing agent could be initially provided and then subsequentlyvaporized for mixing with the treatment gas. The liquid reducing agentcan be vaporized, for example, by absorbing heat from the exothermicreduction reaction, absorbing heat from the reactor (the reactor may beheated via power deposition that occurs during plasma generation), or byproviding heating means in the plasma chamber. A minimal amount ofvaporized liquid reducing agent sufficient for initiating the reductionreaction may be present in the plasma reactor without the need for anyexternal heating. Illustrative liquid reducing agents include water;high vapor pressure (e.g., at least about 0.1 mm Hg) hydrocarbons suchas alcohols (e.g., C₂-C₆ alkanols such as ethanol and isopropanol),ketones (e.g., C₂-C₆ alkyl ketones such as acetone, methyl ethyl ketone,and diethyl ketone), and alkanes (e.g., C₆-C₁₂ alkyls such as hexane,heptane, octane, and nonane); and olefins (e.g., alkenes such as hexeneand heptene). In addition, a gaseous or solid reducing agent could beinitially dissolved in a carrier liquid and then vaporized or releasedfrom the carrier liquid for the plasma reaction. For example, an ammoniaor hydrazine reducing agent could be dissolved in water. Suchgas-containing or solid-containing liquids are also referred to hereinas “liquid reducing agents.” According to a particular embodiment, thereducing agent is H₂O vapor when the halogen-containing gas is F₂. Incertain variants, a liquid reducing agent (such as H₂O) that isvaporized is the only reducing agent that is present.

According to certain embodiments, a non-aqueous, gaseous reducing agentis mixed with the treatment gas. A non-aqueous, gaseous reducing agentmay substantially reduce the amount of electrical energy required tofully reduce the halogen-containing gas. According to an alternativeembodiment, the reducing agent is H₂ when the halogen-containing gas isF₂.

The relative amount of reducing agent mixed with the halogen-containinggas may vary considerably. According to a particular embodiment, therelative amount may vary from about 0.5:1 to about 4:1 H₂:halogen atommolar ratio. In the case of H₂ as the reducing agent and F₂ as thehalogen-containing gas, the molar ratio may be about 1:1 (which equatesto 1:1 by volume concentration ratio). In particular, the volumeconcentration of H₂ introduced into the F₂-containing treatment gas maybe at least equal to the volume concentration of F₂. Avoiding possibleexplosive conditions is also a consideration in the F₂/H₂ mix ratio.Options for eliminating explosive conditions may include diluting the H₂with an inert gas, adding H₂ gradually to the F₂-containing stream, andadding excess H₂ above the amount that could be consumed in thereduction reaction.

In the case of H₂O as the reducing agent and F₂ as thehalogen-containing gas, the molar ratio of hydrogen atom:fluorine atomin certain embodiments may be about 0.5:1 to about 2:1.

The reducing agent may be mixed with the halogen-containing gas in anysuitable manner. Complete mixing may be achieved prior to generating theplasma. Alternatively, the reducing agent may be gradually mixed withthe halogen-containing gas during plasma generation. Such gradual mixingmay reduce exothermic heat generation and assist in avoiding explosiveconditions. The mixing may be accomplished with any known mixingprocedures or devices such as, for example, static mixing, nozzles,baffles or a packed bed.

The temperature and pressure of the treatment gas and the reducing agentat the point of mixing are not critical. The treatment gas, for example,can be at the temperature and pressure that exist in the effluent streamfrom any processing module. Typically, the treatment gas and thereducing agent are at ambient temperature and pressure.

Although not bound by any theory, it is believed that the reducing agentreduces the halogen-containing gas via a reaction involving generating ahydrogen radical (H.) in the presence of the plasma. The hydrogenradicals dissociate a free halide gas (e.g., F₂) or react with a halogenatom in a halogenated hydrocarbon. By way of example, a disassociativereduction pathway is illustrated below with reference to F₂ reduction byH₂ in a non-thermal reactor in the presence of water.e⁻+F₂→2F.  (1)e⁻+H₂→2H.  (2)H.+F₂→HF+F.  (3)F.+H₂→HF+H.  (4)F.+H₂O→HF+.OH  (5).OH+H₂→H₂O+H.  (6)If the reducing agent is H₂, a chain reaction is propagated (seereactions (3) and (4) above). If the reducing agent is H₂O rather thanH₂, the plasma (e⁻) generates H. radicals from the H₂O resulting ingreater energy consumption.

The chain propagation depicted above, in essence, provides a continuoussource of hydrogen radicals that requires less energy to generate thanin the case of employing water alone as the reducing agent. It should benoted that reactions (5) and (6) are optional since the presence ofwater is not required in all of the disclosed embodiments.

Other possible specific reductions and reduction products include:CFCs+H₂→HF+HCl+completely or partially dehalogenated hydrocarbonsH₂+SiF₄→HF+silane or various fluorosilanesCCl₄+H₂→HCl, methane and various chloromethanes

It is also possible to add O₂ to the feed gas mixture in the plasma inthese reductions to oxidize the hydrocarbons. The complete reactionsthen would be:CFCs+H₂+O₂→HF+CO₂+H₂O+HF+HClSiF₄+H₂+O₂→HF+H₂O+SiO₂CCl₄+H₂+O₂→HCl+H₂O+CO₂

Reduction of other halogen-containing feed gas can result in a varietyof additional gaseous reduction products.

According to certain embodiments of the processes, at least one of thereduction products for each particular halogen-containing treatment gasis substantially water-soluble or at least more water-soluble than thehalogen-containing treatment gas. Such water-soluble gaseous reductionproducts can be dissolved in water for further treatment. For example,HF gas can be scrubbed and the resulting HF-containing water can beneutralized with a base. One particular neutralization method for HFacid involves treating the HF acid in a calcium or sodium alkalinescrubber to produce calcium or sodium fluoride. The calcium or sodiumfluoride may be subsequently processed and sent to a landfill or used asan additive for dental treatments. Other separation techniques such as awater bubbler or water spray contactor may also be used for removinggaseous reduction products that are not intended for emission into theatmosphere. As described in more detail below, the scrubbing of thegaseous reduction product may occur at least partially within the plasmareactor. Alternatively, the scrubbing may be performed downstream fromthe plasma reactor in a separate unit. Such scrubbing is well-known andany suitable devices or processes may be used.

The liquid present during the plasma generation and reduction reactionmay be any liquid that has heat absorbing and gas-solvatingcharacteristics. According to certain embodiments, this liquid can alsoserve as the source for the reducing agent. Illustrative heat-absorbingliquids include those that have a low boiling point such as, forexample, less than about 150° C. and a high heat of vaporization suchas, for example, at least about 35 kJ/mole. Additional liquids includethe liquid reducing agents identified above. Water is the typicalliquid, but other liquids such as alcohols, light oils, waxes or otherhydrocarbons may be used. When F₂ is the treatment gas the water mayinclude particles of calcium hydroxide in the form of a slurry or may bea solution of sodium hydroxide. Calcium hydroxide and sodium hydroxidereact with HF and, thus, would promote additional scrubbing of the HFfrom the product gas stream in the plasma reactor.

The heat absorbed by the liquid causes at least a portion of the liquidto evaporate into the gas phase (e.g., steam in the case of water). Thisheat absorption/evaporation mechanism prevents significant increases inthe temperature of the bulk gas mixture undergoing treatment. Forexample, in certain embodiments the temperature of the bulk gas mixturedoes not exceed about 100° C. Since no heat is externally applied, theoverall operating conditions of these embodiments does not exceed about100° C.

If the liquid is a reducing agent, liquid vapor generated by theevaporation can mix with the halogen-containing gas and react to reducethe halogen-containing gas. Typically, only a portion of the liquid,rather than substantially all of the liquid, is evaporated for reducingthe halogen-containing gas. The remaining portion of the liquid,therefore, is available for additional heat absorption and solvating ofthe water-soluble reaction products. Evaporation of the liquid in theplasma chamber also results in more gradual mixing of the reducing agentvapor with the treatment gas. Slower mixing of the reducing agentminimizes the explosion risk, and reduces the maximum temperatureencountered in the plasma reactor system. The amount of evaporation canbe controlled, for example, by appropriately adjusting the temperatureof the treatment gas that is in contact with the liquid and/or thetemperature of the liquid. The temperature of the liquid may becontrolled, for example, by preheating the liquid prior to itsintroduction into the plasma chamber or by heating a surface in theplasma chamber over which the liquid flows.

The plasma may be generated by any energy supply source known in theart. For example, the plasma could be energized by radio frequency (RF),microwave, laser, electrical discharge, or a combination thereof. Myriadreactor configurations are known for each type of plasma and any suchgeometry may be suitable for effecting the disclosed processes.According to particular embodiments of the disclosed processes, theplasma is a non-thermal plasma.

A basic distinction between non-thermal plasmas and thermal plasmas isdescribed above. Other possible characteristics of non-thermal plasmasare that some non-thermal reactors have a relatively small footprintsince they operate at atmospheric pressure. In addition, the powersources are relatively simple AC or DC sources.

The plasma operating conditions may vary depending upon the type ofplasma employed. Non-thermal plasmas typically operate from sub-ambienttemperature up to at least about 600° C., but the temperature of thebulk gas in the plasma may vary depending on the temperature of theincoming feed gas or as the result of any enthalpy released from thechemical reactions occurring in the plasma. For example, the disclosedreduction of F₂ is an exothermic reaction and, thus, the temperature ofthe bulk gas in the plasma may rise to about 500 or 600° C. However,this temperature can be reduced to less than or equal to about 100° C.by generating the plasma in the presence of a liquid that can absorb theheat as described below in more detail.

The operating pressure for non-thermal plasmas may vary. For example,glow discharge non-thermal pressures typically operate at subatmosphericpressures such as, for example, about 1 mTorr to about 50 Torr. Silentdischarge reactors and pulsed-DC reactors (described below in moredetail) typically operate at slightly sub-ambient to slightlyabove-ambient pressure such as, for example, about 0.5 atmospheres toabout 10 atmospheres. The power required to generate the non-thermalplasma may vary depending upon the feed gas flow rate and the type ofhalogen-containing gas undergoing treatment. It is known that, ingeneral, the specific power may be calculated by the equation: (volumeflow rate×energy/volume=power). For example, in the embodiment of about1:1 H₂:F₂ volume % in the feed gas stream, substantially completereduction of F₂ occurs at about 80 to about 150 J/L feed gas. Thisequates to approximately 1 kW of power required per 400 L/minute of feedgas. In the embodiment of H₂O as the reducing agent, based on calculatedestimates, an energy deposition of about 10-20 kJ/L feed gas may berequired, which equates to about 56 kW of power to treat 400 L/minute offeed gas.

Although any type of non-thermal plasma-generating system may beutilized for the disclosed processes, there are two types that may beespecially suitable since they are capable of generating non-thermalplasmas at ambient pressure. These two non-thermal plasma-generationsystems are referred to herein as a silent discharge reactor (also knownin the art as “dielectric barrier discharge reactor”) and a pulsed-DCreactor, respectively. The general geometry and operation of suchreactors is described below. An additional, particularly useful, plasmareactor embodiment is referred to herein as a “film discharge reactor”.It should be recognized that film discharge reactors may be usefulregardless of the type of plasma-generation system employed. In otherwords, a silent discharge system may be combined with film dischargereactor geometry resulting in a silent-discharge, film reactor. Thegeneral geometry and operation of a film discharge reactor is alsodescribed below.

In a silent discharge reactor, at least one high voltage electrode islocated a distance from at least one opposing ground electrode. The gapsbetween the high voltage electrodes and the opposing ground electrodesdefine a passage through which a gas flows. A dielectric material isdisposed on the surface of the high voltage and/or ground electrodes. Avoltage is applied to the high voltage electrode to generate anon-thermal plasma discharge in the gap between the high voltageelectrode and the ground electrode. The non-thermal plasma is maintainedby applying an AC voltage to the high voltage electrode.

In a pulsed-DC reactor, a high voltage electrode is located a distancefrom an opposing ground electrode. The gap between the high voltageelectrode and the opposing ground electrode defines a passage throughwhich a gas flows. There is no dielectric material disposed on anysurface. A voltage is applied to the high voltage electrode to generatea non-thermal plasma discharge in at least a portion of the gap betweenthe high voltage electrode and the ground electrode. The non-thermalplasma is maintained by applying a pulsed DC voltage to the high voltageelectrode. The pulsed DC voltage ramps up and down very quickly (e.g., ananosecond). In general, pulsed-DC reactor systems tend to be moreexpensive than silent discharge reactors due to the relatively elaboratepower supply configuration required for pulsed-DC reactors.

In both the silent discharge reactor and the pulsed-DC reactor, when theelectric field reaches a sufficient level, electrons are accelerated tothe point that they will collide with, and ionize, gas molecules. Eachsuch collision produces a charged molecule (i.e., ion) and oneadditional electron. This continuing process multiplies the number ofelectrons in the gap (referred to in the art as “avalanches”). In thecase of a silent discharge reactor the avalanche (also known as“microstreamers”) continues until it impacts a dielectric materialbarrier. The charge accumulation at the dielectric material barriereffectively quenches the avalanche, thereby avoiding formation of an arcor thermal plasma. When the AC polarity at the high voltage electrodereverses, the process repeats itself. In the case of a pulsed-DCreactor, the end of the DC pulse extinguishes each avalanche. Theelectrons generated in such plasmas react with the gases in the gap asdescribed above.

In a film discharge reactor, a first electrode is located a distancefrom a film or body of liquid that contacts or immerses an opposingsecond electrode or a dielectric barrier disposed on the secondelectrode (referred to herein as the “wetted electrode”). The liquidfilm may be flowing over at least a portion of the boundary of thesecond electrode. Alternatively, the second electrode may be disposed ina liquid bath or reservoir that may or may not be flowing. The spacebetween the first electrode and the opposing second electrode defines apassage through which a treatment gas flows. According to the disclosedprocesses, the treatment gas flows over the surface of the liquid and aplasma is generated in the gas region between the first electrode andthe liquid surface, particularly at or near the surface of the liquid.The plasma radicals and the reduction products may contact the surfaceof the liquid. The liquid film in a film discharge reactor can absorbthe heat generated by the exothermic reduction reaction, at leastinitially dissolve the water-soluble reaction products, and serve as thesource of the gaseous reducing agent, as mentioned above.

The plasma can be generated in a device containing any type ofgeometrical-shaped electrodes. General classes of potential devicesinclude parallel plate (horizontal or vertical) reactors, cylindricalplasma reactors, and reactors containing arrays of tubular electrodes.One example of a possible non-thermal, film discharge reactorconfiguration is shown in U.S. Pat. No. 5,980,701. A few particularembodiments of possible non-thermal, film discharge reactors aredescribed below.

One embodiment of a non-thermal, film discharge reactor is shown inFIG. 1. A chamber 10 defines an upper portion 11, a lower portion 12,side wall 15, top wall 22, bottom wall 23, and an interior void 18. Thechamber 10 depicted in FIG. 1 is cylindrical but it could be anothershape such as conical or rectangular. At least one first electrode 13 isreceived within the upper portion 11 of the chamber 10. A dielectricbarrier coating or sheath 14 may be provided on the surface of the firstelectrode 13. The dielectric barrier coating 14 may encapsulate all or asubstantial portion of the first electrode 13. The first electrode 13may be made from any type of conductive material known in the art suchas, for example, graphite, vitreous carbon, stainless steel, or othermetals, or a conductive salt solution. The dielectric barrier coating 14may be made from any type of known dielectric material such as alumina,perfluorinated polyethylene, quartz, glass, or other metal oxides. Inone approach, the first electrode 13 is formed from a hollow tubedefining an interior cavity into which is disposed a conductive materialfibrous matrix or mesh such as, for example, stainless steel wool. Thewalls of the hollow tube may be constructed from a dielectric materialthat functions as the dielectric barrier 14. The dielectric barriercoating 14 should be sufficiently thick to prevent dielectric breakdownof the dielectric material at the operating fields of the device. Forexample, the dielectric barrier coating may be a thin film (i.e., lessthen 0.1 mm thick) up to about 0.25 inches thick, with one range beingabout 1 to about 6 mm thick. The first electrode 13 coated with thedielectric barrier 14 may have any shape such as an elongated rod, awire or an elongated plate.

At least one second electrode 16 is located at the side-walls 15 of thechamber 10. The second electrode 16 is disposed within the chamber 10 inthe sense that it may define the side-walls 15 or it could be disposedon an inside surface 17 of the side-walls 15. The second electrode 16may have any shape such as a tubular plate extending around thecircumference of the cylindrical chamber 10, circular rods extendingaround the circumference of the cylindrical chamber 10, an elongated,substantially planar plate, or a porous material such as a fabric orfoam-like material. Although not shown, the second electrode 16 mayinclude a dielectric barrier coating or sheath.

According to the embodiment of FIG. 1 an AC voltage source (not shown)is operatively coupled to first electrode 13 and the second electrode 16is grounded (or connected to a low voltage source (not shown)). Thus,first electrode 13 is the high voltage or “hot” electrode and the secondelectrode 16 is the ground electrode. Alternatively, the AC voltagesource could be coupled to the second electrode 16 and the firstelectrode 13 could serve as the ground electrode. The first electrode 13and the second electrode 16 are positioned in an opposing relationshipso that an electric field can be generated in the void or gap betweenthe first electrode 13 and the second electrode 16.

In general, the plasma reactor chamber defines at least one inlet forintroducing a feed gas into the interior void of the chamber. Accordingto one variant (not shown), there are only inlets for receiving a feedgas that is a mixture of the treatment gas and the reducing agent gas.In other words, the treatment gas and the reducing agent gas arepre-mixed prior to entering the plasma reactor chamber. Alternatively,the inlet(s) receives a feed gas that consists of only the treatment gasin embodiments in which the reducing agent is generated from the liquidfilm. According to another variant (depicted in FIG. 1), the treatmentgas and the reducing agent are mixed in the plasma reaction chamber. Ofcourse, pre-mixing and inchamber mixing could both be used in a system.

In particular, there is at least one inlet 19 for introducing thetreatment gas into the interior void 18 of the chamber 10. Inlet 19 maybe located at any position in the chamber such as the top wall 22 of thechamber 10 as illustrated in FIG. 1 or in the bottom wall 23 of thechamber 10. Another option is to provide a first electrode 13 thatdefines pinholes for introducing the treatment gas. Inlet 19 is in fluidcommunication with a source of treatment gas.

There is also at least one optional inlet 20 for introducing thereducing agent into the interior void 18 of the chamber 10. Inlet 20also may be located at any position in the chamber 10. In the FIG. 1embodiment, the side-walls 15 and second electrode 16 define inlets 20.For example, the side-walls 15 and/or second electrode 16 can be made ofa porous or foam-like material or they can define pinholes through whichthe reducing agent gas can flow. In the case of the side-walls 15, theporous material can be made of alumina, perfluorinated polyethylene(e.g., Teflon®), glass or other metal oxides. The inlets 20 may bearranged along the axial length of the cylindrical chamber 10 so thatthe reducing agent can be gradually introduced into the treatment gasstream as it flows through the chamber 10. Inlet 20 is in fluidcommunication with a reducing agent source.

The interior void 18 of the chamber 10 includes a liquid region 21 thatis contiguous with the inside surface 17 of the side-walls 15 andpartially fills the interior void 18. The liquid region includes aliquid surface 30 facing the interior void 18 of the chamber 10. Aheat-absorbing liquid such as described above occupies liquid region 21during operation of the plasma reactor. The liquid region 21 depicted inFIG. 1 is in the form of a liquid film that gravity flows along theinside surface 17 of the side-walls 15. The liquid film is maintainedwithin liquid region 21 via surface tension. The inside surface 17 ofthe side-walls 15 may be provided with grooves or other types oftexturing for promoting the uniformity of the liquid film.

Two examples of side-wall 15/liquid region 21 configurations are shownin FIGS. 2 and 3, respectively. Both FIGS. 2 and 3 illustrate horizontalelectrode embodiments as opposed to the cylindrical vertical embodimentof FIG. 1. But the ground electrode, liquid region and reducing agentintroduction arrangements depicted in FIGS. 2 and 3 may also be utilizedfor the side-wall 15/liquid region 21 of FIG. 1. In particular, thedesign in FIG. 2 is provided with a first section 50 that includes firstelectrodes 51, a diffuser 52 through which the reducing agent can flow,and a liquid region 53. The first section 50 is an example of a possiblearrangement for the side-wall 15/liquid region 21 of FIG. 1. Similarly,the design in FIG. 3 is provided with a first section 70 that includesfirst electrodes 71, a liquid region 72, and an electrochemical cell 73for producing a reducing agent gas. The embodiments shown in FIGS. 2 and3 are described below in more detail.

Referring back to FIG. 1, the top wall 22 of the chamber 10 defines aninlet port 24 for introducing the liquid into the liquid region 21. Thebottom wall 23 of the chamber 10 defines an outlet port 26 through whichthe liquid exits from the chamber 10.

The interior void 18 of the chamber 10 also may optionally include agas-scrubbing region 27 that is populated with gas-scrubbing packingmaterial 28. The gas-scrubbing packing material 28 may be any type ofmaterial that is known to provide increased surface area for gas/liquidexchange. Illustrative gas-scrubbing packing material particularlysuitable for HF include perfluorinated polymeric materials such asperfluorinated polyethylenes or polyvinylidene fluoride. Liquid may beprovided to the gas-scrubbing packing material 28 by draining the liquidfrom the liquid region 21 through the gas-scrubbing packing material 28.Optional liquid sprayers 25 may also be provided at the side-walls 15 ofthe chamber 10.

The chamber 10 also includes at least one outlet 29 for exhausting theproduct gas mixture from the chamber 10. The outlet 29 may be located atany position in the chamber 10 such as, for example, in the lowerportion 12 of the chamber 10 as shown in FIG. 1. In a variant that hasthe treatment gas inlet 19 located in the lower portion 13 of thechamber 10, the exhaust or product gas outlet 29 typically is located inthe upper portion 11 of the chamber 10.

During operation of the plasma reactor of FIG. 1 a treatment gas willflow through inlets 19 and then vertically down along the length of void18 in the chamber 10. The treatment gas includes a halogen-containinggas such as F₂ and may include other gases such as N₂. A reducing agentgas such as H₂ may optionally flow through inlets 20 and into void 18 ofthe chamber 10. The reducing agent gas flowing through inlets 20 bubblesthrough the liquid in the liquid region 21 and mixes into the treatmentgas stream forming a feed gas stream. A liquid such as water may also beflowing through the liquid region 21. The liquid flowing through theliquid region 21 may be the source of the reducing agent as describedabove. The liquid and the gas may be flowing in the same directionthrough the chamber 10 (i.e., co-current flow). The flow rate of thetreatment gas, reducing agent gas, resulting feed gas mixture, andliquid may vary widely depending upon the desired amount of treatmentgas for abatement. For example, the flow rate of the feed gas mixturethrough the chamber 10 may be from about 100 standard cubic centimetersper minute (seem) to about 1500 standard liters per minute. The minimumliquid flow rate for substantially complete wetting of the insidesurface 17 of the side wall 15 may be about 0.03 kg/m-s and the maximumliquid flow rate to remain in a laminar regime of fluid flow is about0.5 kg/m-s in the case of water.

Electric power will be supplied from the AC voltage source to the firstelectrode 13 to generate a non-thermal plasma in the feed gas mixturepresent in the gap between the first electrode 13 and the secondelectrode 16. The frequency applied to the first electrode 13 may varydepending upon the feed gas flow rate and halogen concentration. Theapplied frequency, for example, may range from about 30 Hz to about 5000Hz, particularly about 50 Hz to about 1000 Hz. The voltage applied tothe first electrode 13 may vary depending on the gap distance betweenthe first electrode 13 and the second electrode 16, the types of gas inthe feed gas, and the temperature and pressure of the system. Theapplied voltage should be sufficient to at least reach onset voltage asis understood in the art. As an example, a voltage of about 10 to about30 kV may be applied to the first electrode 13 when the gas in theelectrode gap is a mixture of F₂, N₂ and the reducing agent (e.g., H₂and/or H₂O), and the electrode gap width is about 0.1 to about 3 cm.According to an illustrative embodiment when the plasma is generated atatmospheric pressure, the electrode gap width may be about 0.1 cm toabout 0.8 cm. The electrode gap width may be substantially constant overthe length of the reaction zone or it may vary, for example, by up toabout 25%.

The reduction reaction in the plasma-excited feed gas mixture will occurat or near the interior surface 30 of the liquid region 21.Consequently, the exothermic heat from the reduction reaction will beabsorbed by the liquid in the liquid region 21. The heat absorption maybe sufficient to vaporize a portion of the liquid, but the continuousfeed of flowing liquid will replace any vaporized portion. The vaporizedliquid, if it is not a reducing agent that has reacted with thehalogen-containing gas, enters the void 18 of the chamber 10 and isexhausted with the product gas stream via exhaust gas outlets 29. Aportion of the liquid in the liquid region 21 may also be vaporized by aheating element (not shown) disposed within or adjacent to the secondelectrode 16. Other possible heating means include a jacket around thechamber 10. If the vaporized liquid is a reducing agent, the vapor canmix and react with the halogen-containing gas in the electrode gap.

At least a portion of the water-soluble gaseous reduction product (suchas HF) formed in the void 18 of the chamber 10 will be scrubbed from thegas stream as it progresses down the vertical axial length of chamber10. In particular, a portion of the gaseous reduction product maydissolve in the liquid of the liquid region 21 as it flows down theinside surface 17 of the side wall 15. A portion of the gaseousreduction product also dissolves in the liquid provided in thegas-scrubbing region 27.

The exhaust gas exiting through outlet 29 may include any reductionreaction product that was not removed from the scrubbing action in thechamber 10 (such as HF), non-reducible gases that were present in thetreatment gas (such as N₂), and excess reducing agent (such as H₂). Theliquid exiting through outlet port 26 may include dissolved reductionproducts (such as HF).

It will be appreciated that there could be variations of a cylindrical,non-thermal, film discharge reactor similar to that depicted in FIG. 1.For example, the treatment gas could flow into the chamber at the bottomof the chamber and the product gas exit at the top of the chamber. Insuch a variant, the liquid flowing down the inside surface 17 of theside wall 15 will be moving countercurrent to the flow of the gas. Thismay provide improved absorption of the reduction product into theliquid.

Another option is to not provide the scrubbing packing material 28 inthe interior void 18 of the chamber. In this case, partial scrubbing ofthe reduction product in the liquid of the liquid region 21 likely willoccur, but the product gas exhausting from the chamber will include agreater concentration of reduction product gas. Such remaining reactionproduct gas could simply be scrubbed in a downstream module.

As mentioned above, both FIGS. 2 and 3 illustrate examples of theelectrode arrangement in horizontal, silent-discharge, film reactors.FIG. 2 depicts an embodiment wherein the reducing agent gas is suppliedfrom a source (not shown) external to the reactor. FIG. 3 shows analternative approach for supplying the reducing agent that involvesintegrating an electrochemical cell into the plasma reactor structure.Another possibility is to provide the plasma reactor with a H₂ reformer.

In particular, FIG. 2 depicts first electrodes 51 that are surrounded bya liquid 25 region 53. The liquid region 53 is bounded or supported on alower side 54 by a diffuser 52. The liquid region 53 has an uppersurface 55. Second electrodes 56 are located a distance above the uppersurface 55 of the liquid region 53 in an opposing relationship relativeto the first electrodes 51. A dielectric barrier coating or sheath 57 isdisposed on the surface of second electrodes 56. The first and secondelectrodes 51 and 56, dielectric barrier 57, and liquid in the liquidregion 53 may be comprised of the same materials as described above inconnection with FIG. 1. The diffuser 52 may be made of any porous orfoam-like material that includes microvoids for allowing passage ofreducing agent gas molecules 58 to bubble into the liquid. In FIG. 2,first and second electrodes 51 and 56 are in the shape of cylindricalrods, but both or either electrodes 51 and 56 could have other shapessuch as, for example, planar plates. If first electrode 51 is planar inshape it can be provided with pinholes or microvoids (such as in aporous material or mesh) for allowing passage of the reducing agent gas.It will be understood that the rod-shaped electrodes 51 and 56 have anaxial length extending out from, and into, the plane of the drawingsurface of FIG. 2.

It will be appreciated that the representation in FIG. 2 shows only aportion of a horizontal plasma reactor. First region 50 and secondelectrodes 56 may be housed inside a chamber. The rod-shaped electrodes51 and 56, and the diffuser 52 may be connected to a wall of suchchamber for support. The chamber, of course, would include inlets andoutlets for the treatment gas, reducing agent gas, product or exhaustgas and the liquid. An AC voltage source (not shown) is operativelycoupled to second electrodes 56 and the first electrodes 51 are grounded(or connected to a low voltage source (not shown)). Thus, secondelectrodes 56 are the high voltage or “hot” electrode and the firstelectrodes 51 are the ground electrodes. Alternatively, the AC voltagesource could be coupled to the first electrodes 51 and the secondelectrodes 56 could serve as the ground electrodes. The first electrodes51 and the second electrode 56 are positioned in an opposingrelationship so that an electromagnetic field can be generated in thevoid or gap 59 between the first electrodes 51 and the upper surface 55of the liquid region 53.

During operation a treatment gas will flow in the gap 59 and mix withreducing agent gas bubbling out of the upper surface 55 of the liquidflowing through the liquid region 53 to form a feed gas mixture. Asilent discharge plasma will be generated in the feed gas mixture in thegap 59 to initiate and sustain the reduction of the halogen gas in thetreatment gas. The resulting product gas then will exit the chamber viaan exhaust gas outlet. The feed gas flow direction and liquid flowdirection may both be parallel along the axial length of the electrodes51 and 56 (i.e., co-current flow) or there may be countercurrent flow.Alternatively, the feed gas flow direction and the liquid flow directionmay be perpendicular (or at some other angle) relative to the eachother. In this case, either the feed gas flow direction or the liquidflow direction would be perpendicular or angled relative to the axiallength of the electrodes 51 and 56.

FIG. 3 depicts first electrodes 71 that are surrounded by a first liquidregion 72. An electrochemical cell 73 for generating a reducing agentsuch as H₂ is located adjacent to the first liquid region 72. Theelectrochemical cell 73 includes an electrochemical ground electrode 74,a membrane 75, and a cathode 76 and is immersed in a second liquidregion 77 (e.g., water). The electrochemical cell 73 generates H₂molecules 78 and O₂ molecules 79 based on well known principles. Themembrane 75 may be angled relative to the plane of the cathode 76 toflow the O₂ molecules 79 in the direction indicated in FIG. 3. Theelectrochemical ground electrode 74 and cathode 76 may be made from anytype of conductive material known in the art such as, for example,graphite, vitreous carbon, stainless steel, other metals, or aconductive salt solution. The membrane 75 may be made from any ionexchange material known in the art such as, for example, perfluorinatedpolymers (e.g., Nafion® available from E.I. du Pont).

Electrochemical ground electrode 74 partitions first liquid region 72and second liquid region 77. The respective liquids in first liquidregion 72 and second liquid region 77 may be the same or different.According to a particular embodiment, the liquid is water in both firstliquid region 72 and second liquid region 77.

The first liquid region 72 may be bounded or supported on a lower side80 by the electrochemical ground electrode 74. The first liquid region72 has an upper surface. Second electrodes 82 are located a distanceabove the upper surface 81 of the first liquid region 72 in an opposingrelationship relative to the first electrodes 71. A dielectric barriercoating or sheath 83 is disposed on the surface of second electrodes 82.The first and second electrodes 71 and 82, dielectric barrier 83, andliquid in the first liquid region 72 may be comprised of the samematerials as described above in connection with FIG. 1. In FIG. 3, firstand second electrodes 71 and 82 are in the shape of cylindrical rods,but both or either electrodes 71 and 82 could have other shapes such as,for example, planar plates. If first electrode 71 is planar in shape itcan be provided with pinholes or microvoids (such as in a porousmaterial or mesh) for allowing passage of the reducing agent gas. Itwill be understood that the rod-shaped electrodes 71 and 82 have anaxial length extending out from, and into, the plane of the drawingsurface of FIG. 3.

It will be appreciated that the representation in FIG. 3 shows only aportion of a horizontal plasma reactor. First region 70, secondelectrodes 82 and electrochemical cell 73 may be housed inside achamber. The rod-shaped electrodes 71 and 82, and the electrochemicalcell 73 parts may be connected to a wall of such chamber for support.The chamber, of course, would include inlets and outlets for thetreatment gas, reducing agent gas, product or exhaust gas and theliquids. An AC voltage source (not shown) is operatively coupled tosecond electrodes 82 and the first electrodes 71 are grounded (orconnected to a low voltage source (not shown)). Thus, second electrodes82 are the high voltage or “hot” electrode and the first electrodes 71are the ground electrodes. Alternatively, the AC voltage source could becoupled to the first electrodes 71 and the second electrodes 82 couldserve as the ground electrodes. The first electrodes 71 and the secondelectrode 82 are positioned in an opposing relationship so that anelectromagnetic field can be generated in the void or gap 84 between thefirst electrodes 71 and the upper surface 81 of the first liquid region72. A DC power supply that operates at low voltage and moderate currentmay be coupled to the electrochemical cathode 76.

During operation a treatment gas will flow in the gap 84 and mix withreducing agent gas bubbling out of the upper surface 81 of the liquidflowing through the liquid region 72 to form a feed gas mixture. Asilent discharge plasma will be generated in the feed gas mixture in thegap 84 to initiate and sustain the reduction of the halogen gas in thetreatment gas. The resulting product gas then will exit the chamber viaan exhaust gas outlet. The feed gas flow direction and liquid flowdirection may both be parallel along the axial length of the electrodes71 and 82 (i.e., co-current flow) or there may be countercurrent flow.Alternatively, the feed gas flow direction and the liquid flow directionmay be perpendicular (or at some other angle) relative to the eachother. In this case, either the feed gas flow direction or the liquidflow direction would be perpendicular or angled relative to the axiallength of the electrodes 71 and 82.

Another silent discharge plasma reactor that can be used to perform thedisclosed processes is represented in FIG. 4. An inner cylindricalelectrode 100 is received within an outer tubular electrode 101. Theouter cylindrical electrode 101 defines an inner surface 102 thatsupports a first dielectric barrier 103. The inner cylindrical electrode100 defines an outer peripheral surface 104 that supports a seconddielectric barrier 105. The inner surface 102 of the outer electrode 101and the outer surface of 104 of the inner cylindrical electrode 100define an annular gap 106. According to another embodiment, only one ofthe first or second dielectric barriers 103, 105 is present. Adielectric packing material may be received within at least a portion ofthe annular gap 106. Illustrative dielectric packing materials includequartz, alumina, titania, other non-conductive ceramics, and fluorinatedpolymers. The electrodes 100 and 101 and the dielectric barriers 103 and105 may be made with any of the materials described above in connectionwith the embodiments shown in FIGS. 1-3.

An AC voltage source (not shown) is operatively coupled to innercylindrical electrode 100 and the outer tubular electrode 101 isgrounded (or connected to a low voltage source (not shown)). Thus, innercylindrical electrode 100 is the high voltage or “hot” electrode and theouter tubular electrode 101 is the ground electrode. Alternatively, theAC voltage source could be coupled to the outer tubular electrode 101and the inner cylindrical electrode 100 could serve as the groundelectrode. An electromagnetic field can be generated in the annular gap106.

During operation a feed gas mixture that includes the treatment gas andthe reducing agent gas enters the reactor through an inlet (not shown)and flows through the annular gap 106. A silent discharge plasma isgenerated in the feed gas mixture in the annular gap 106 to initiate andsustain the reduction of the halogen gas in the treatment gas. Theresulting product gas then will exit the reactor via an exhaust gasoutlet (not shown).

FIG. 8 shows a further embodiment of a treatment reactor 250 that iscapable of treating and abating the treatment gas comprising a plasmacell 235 and a scrubbing cell 230. The plasma cell 235 is adapted toenergize the treatment gas to form a plasma in the treatment gas,thereby inducing abatement reactions and other reactions in thetreatment gas. The scrubbing cell 230 is adapted to contact thetreatment gas with a scrubbing fluid to scrub or remove unwantedparticulates and hazardous components from the treatment gas stream.Thus, the plasma cell 235 and scrubbing cell 230 cooperate to treat thetreatment gas to generate a treated flow stream that is more easilyfurther refined or that may be released into the atmosphere withoutadverse environmental effects. In addition, the plasma may be formedwhile injecting a fluid such as water into the plasma. This provides asynergistic effect in which the water based plasma can more effectivelytreat the treatment gas to reduce the hazardous and toxic productstherein.

The treatment reactor 250 includes a plasma cell 235 and a scrubbingcell 230 that are coaxially disposed to each other. The co-axial plasmaand scrubbing cells 235, 230 are centered about the substantially sameaxis, and preferably, symmetrical about the axis as well. For example,at least a portion of the plasma cell 235 may be surrounded by thescrubbing cell 230, as shown in FIG. 8. Alternatively, at least aportion of the scrubbing cell 230 could be surrounded by the plasma cell235. The coaxial plasma and scrubbing cells 230, 235 can provide aconvoluted treatment flow path through the reactor 250 with a minimumfootprint. This allows for a longer treatment gas residence time in thereactor 250, and consequently, improved abatement of the treatment gas.At the same time, the coaxial cells 230, 235 allow for a fairly compactshape factor thereby reducing the footprint or space required for thereactor 250 in a clean room environment. However, the treatment reactor250 does not have to be used in the clean room and can also be placed inan external non-clean room environment such as a pumping room orotherwise, since the reactor can operate at atmospheric pressure and canpotentially exhaust to atmosphere if the treated effluent is safe.

The coaxial plasma and scrubbing cells 235, 230 are defined by coaxialinner and outer tubes 236, 238. The tubes 236, 238 comprise extendedhollow passageways that are arranged to define the plasma and scrubbingcells 235, 230. In the version shown in FIG. 8, the inner tube 236 formsa common wall between the scrubbing and plasma cells 230, 235 that atleast partially surrounds and defines an inner passage 277 comprisingthe plasma cell 235, while the outer tube 238 is spaced apart from theinner tube 236 to define an outer passage 278 comprising the scrubbingcell 230 in the volume therebetween. The tubes 236, 238 comprise a crosssection that is suitable for the flow of treatment gas through thetreatment reactor 250, such as for example, a round, rectangular,triangular or other shape or combination of shapes. For example, thetubes 236, 238 may comprise concentric cylinders having a substantiallycircular cross-section that defines concentric cylindrical plasma andscrubbing chambers 235, 230. The outer tube 238 may further extendbeyond the inner tube 236 and comprise capped upper and lower ends281,282, to define a treatment gas passageway 240 that facilitates flowof the treatment gas between the cells.

The treatment gas can be introduced into the treatment reactor 250 bytreatment gas inlets 223 located upstream of the plasma cell 235. Thetreatment gas introduced into the reactor 250 flows through the plasmacell 235 and undergoes abatement reactions induced by the plasma formedin the plasma cell 235. The plasma treated gas flows through the gaspassageway 240 and into the scrubbing cell 230 where the gas is scrubbedbefore the treated effluent is released from the reactor 250 via theeffluent outlet 248 located downstream of the scrubbing cell 230. In theversion shown in FIG. 8, the treatment gas is introduced through thetreatment gas inlets 223 and flown into a coaxially interior plasma cell235. The reactor 250 comprising the coaxially interior plasma cell 235and external scrubbing cell 230 can provide better electrical isolationof high voltage flow lines in the reactor 250, thus inhibiting shortcircuiting in the reactor 250. Alternatively, the treatment gas may beintroduced into the internal scrubbing cell 230 before being introducedinto the external plasma cell 235, or the positions of the plasma cell235 and scrubbing cell 230 may be switched and the effluent may beintroduced into the cells 230,235 in another suitable order.

The scrubbing cell 230 is adapted to treat the treatment gas byproviding a scrubbing fluid to scrub or remove particulates and unwantedmaterials from the treatment gas, and/or to add reactive species to thetreatment gas to react with and abate the treatment gas. The scrubbingfluid can also dissolve or react with materials in the treatment gas asthe treatment gas travels through the scrubbing cell 230. For example, ascrubbing fluid comprising water may be introduced into a treatment gascomprising HF to dissolve the HF in the scrubbing fluid and remove theHF from the treatment gas stream. The scrubbing fluid can also removesolid particulates, such as SiO₂, from the treatment gas stream. Thescrubbing fluid is provided to the scrubbing cell 230 by a scrubbingfluid distributor 270 comprising one or more scrubbing fluid inlets 232connected to a scrubbing fluid source 234 by scrubbing fluid conduits271. The scrubbing fluid distributor 270 comprises inlets 232 havingnozzles 233 adapted to spray scrubbing fluid into the treatment gasstream in the scrubbing cell 230. The scrubbing fluid inlets 232 andnozzles 233 can be adapted to spray scrubbing fluid in a direction thatis against or across a flow direction of the treatment flow stream, tobetter scrub the effluent. The scrubbing cell 230 can also optionallyinclude scrubbing beads 290 arranged in the scrubbing cell 230, as shownin FIG. 8, that are soaked or coated in scrubbing fluid to provide alarger scrubbing surface contact area. The scrubbing fluid used to scrubthe treatment gas is removed from the reactor 250 via a fluid outlet 237located near the bottom of the reactor 250. The bottom of the reactor250 can serve as a sump that collects and retains the scrubbed liquid.The liquid in the sump can alter the direction of the flow of treatedgas so that the treated gas flows from the plasma cell 235 and into thescrubbing cell 230 via the gas passageway 240.

The scrubbing cell 230 can include a pre-scrubbing cell 231 throughwhich the treatment gas is passed prior to treatment in the plasma cell235. The pre-scrubbing cell 231 serves to remove unwanted particulatesbefore the treatment gas is introduced into the plasma cell 235, as wellas to add gas or fluid additives, such as reactive gas additives, thatcan be energized with the treatment gas in the plasma cell 235 to abatethe treatment gas. The scrubbing cell 230 can also comprise apost-scrubbing cell 229 that is adapted to scrub the treated gas aftertreatment in the plasma cell 235. The post-scrubbing cell 229 is adaptedto dissolve or wash away particulates and other unwanted materials, suchas the above described HF and SiO₂, that may be formed as products ofthe plasma cell treatment. The reactor 250 can also comprise both apre-scrubbing cell 231 and post-scrubbing cell 229 to scrub thetreatment gas before and after treatment in the plasma cell 235, asshown for example in FIG. 8.

In one exemplary version, the pre-scrubbing cell 231 is disposed aboveone or more of the plasma and post-scrubbing cells 235,230 and isdefined by a volume between the upper capped end 281 of the reactor 250and a sidewall of the reactor 250 that cooperate to form an upperpassage 276 comprising the pre-scrubbing cell 231 therebetween. Forexample, in the embodiment shown in FIG. 8, the prescrubbing chamber isdefined by an annular sidewall 265 that is connected to an inner tube236 surrounding an interior plasma cell 235 to allow a flow of treatmentgas between the pre-scrubbing cell 231 and interior plasma cell 235. Theannular sidewall 265 can be connected to the inner tube 236 via a ledge267 that is sloped to connect to the top of the inner tube 236. Theannular sidewall 265 comprises a suitably sized circumference that maybe greater than that of the inner and outer tubes 236,238, or that maybe smaller than one or more of the tubes 236,238 depending on size andgas flow requirements. For example, the annular sidewall 265 can definea circumference that is greater than that of the inner tube 236, and thesloped ledge 267 of the annular sidewall 265 can form at least a portionof a top wall of the post-scrubbing cell 230, as shown in FIG. 8.

The reactor 250 may optionally comprise a source of additive gas, inaddition or as an alternative to the optional pre-scrubbing cell 230,that is adapted to provide a reactive gas capable of reacting withcomponents of the treatment gas to reduce the hazardous gas content ofthe treatment gas. Desirably, the additive gas is added into thetreatment gas either before or in the plasma cell 235 so the additivegas can be energized to form energized species in the plasma cell 235that react with and abate the treatment gas. In one version, a suitableadditive gas comprises a reducing agent, such as for example one or moreof H₂, H₂O, NH₃, C₂H₄, CH₄ and C₂ H₆. In another version, the additivegas comprises an oxidizing agent, such as for example one or more of O₂,O₃, and C₂H₃OH. The additive gas can be provided in the reactor 250 byan additive gas inlet adjacent to the plasma cell 235 that is coupled toan additive gas source by an additive gas conduit. The additive gasinlet can also provide a non-reactive gas from the additive gas source,such as for example one or more of Ar, He, and Xe. By additive gas it ismeant both gases and vaporized liquids.

The plasma cell 235 is adapted to treat the treatment gas by energizingthe treatment gas and/or additive gas to form a plasma in the cell 235.The treatment gas and/or additive gas can be energized in the plasmacell 235 to form energized plasma species that initiate abatementreactions in the treatment gas to reduce a hazardous gas content of thetreatment gas.

The treatment gas can be energized to form a non-thermal plasma in theplasma cell 235 by a dielectric barrier discharge energizer 212, such asa film discharge gas energizer. The dielectric barrier discharge gasenergizer 212 includes one or more electrodes 214, 216 about the plasmacell 235. In the version shown in FIG. 8, the dielectric barrierdischarge gas energizer 212 includes a first electrode 214 about theinner tube 236 and a second electrode 216 that extends into the volumedefined by the inner tube 236. One or more of the first and secondelectrodes 214, 216 are coupled to a voltage source 218, such as an ACvoltage source that is adapted to provide a voltage that is sufficientlyhigh to bias the electrodes 214, 216 to energize the effluent. Thevoltage source 218 may be adapted to provide a voltage of at least about10 kV, for example from about 10 kV to about 60 kV, and even about 30kV.

The reactor 250 can also include a fluid film inlet 220 to flow a fluidover surfaces in the reactor 250, such as over the surface of at leastone of the electrodes 214,216 to form a fluid film over the electrodes214, 216. In the version shown in FIG. 8, the inner tube 236 includes afirst electrode 214 and the fluid film inlet 220 provides fluid thatflows by gravity over an inner surface 226 of the inner tube 236,thereby at least partially covering the first electrode 214. The powercoupled between the first and second electrodes 214,216 through theoverlying fluid film to the treatment gas generates the non-thermalplasma micro-streamers in the cell 235. In one version, the fluid filmis provided by the scrubbing fluid distributor 270. In this version, thefluid film inlet 220 is connected to the scrubbing fluid source 234 viaa fluid film conduit. In another version, as shown in FIG. 8, the fluidfilm inlet 220 is connected via the fluid film conduit 273 to a separatefluid film source 222. The fluid film inlet 220 may be located in thepre-scrubbing chamber 231, as shown in FIG. 8, or in the plasma chamber235. Spent fluid film is removed from the reactor 250 via the fluidoutlet 237. A fluid film suitable for the dielectric barrier dischargegas energizer 212 comprises, for example, one or more of H₂O, H₂O₂ andCH₂O solutions. In the version shown in FIG. 8 the fluid film is formedover a first electrode 214 that is embedded in a dielectric wall 283that forms at least a portion of the inner tube 236, to protect thefirst electrode 214.

One or more of the inner and outer tubes 236,238 includes a dielectricwall 283 having the electrode embedded therein. The dielectric wall 283may form only a portion of the inner or outer tube 236,238 or the tube236,238 may be substantially entirely made from dielectric material withan electrode embedded therein. In the version shown in FIG. 8, the firstelectrode 214 is embedded in a dielectric wall 283 that forms at least aportion of an inner tube 236 defining the plasma cell 235, and iselectrically coupled to a second electrode 216 that extends into theinterior of the plasma cell 235. The dielectric wall 283 forms a commonwall between the plasma and scrubbing cells 235,230 and protects theembedded first electrode 214 from erosion by energized gas species andother materials in the plasma and scrubbing cells 235,230. Embedding theelectrode 214 in the dielectric wall 283 can also inhibit arcing betweenthe first and second electrodes 214,216 while still allowingelectromagnetic energy to be transmitted through the dielectric wall 283to generate the plasma in the plasma cell 235. The dielectric wall 283can be made of dielectric material comprising a ceramic or polymer, suchas for example one or more of Teflon™ a fluoropolymer available fromDuPont de Nemours, Wilmington, Del.; aluminum oxide, silicon oxide,aluminum nitride, yttrium oxide, doped ceramics, aluminum carbide,silicon carbide and composite materials. Desirably, the thickness of thedielectric material in the dielectric wall 283 covering the firstelectrode 214 is sufficiently thick to protect the electrode 214 fromcorrosion but sufficiently thin to allow electrical power to couplethrough the dielectric wall 283 to form the plasma. For example, thethickness of the dielectric material covering the first electrode 214may be at least about 1 mm, for example from about 1 mm to about 5 mm.The embedded electrode 214 comprises a shape and size that is suitablefor generating the plasma in the plasma cell 235. For example, theembedded electrode 214 can comprise planar sheets, rods, or rings ofconductive material embedded in the dielectric wall 236.

The reactor 250 including the coaxially interior plasma cell 235 andexterior scrubbing cell 230, as shown in FIG. 8, can further include asecond electrode 216 that extends a sufficient length into the volume ofan interior plasma cell 235 to energize a desired volume of treatmentgas in the plasma cell 235. In this version, the second electrode 216extends from the upper capped end 281 of the reactor 250 through thepre-scrubbing cell 231 and into the plasma cell 235, and is at leastpartially surrounded by the inner tube 236 comprising the embedded firstelectrode 214. The second electrode 216 includes a rod-shaped metalelectrode or other metallic structure suitable to couple energy to thetreatment gas in the plasma cell 235. The second electrode 216 can alsobe at least partially embedded in a dielectric cover 294 that protectsthe embedded second electrode 216 by inhibiting corrosion of theembedded electrode and by reducing arcing between the first electrode214 and second electrode 216. The spacing between the second electrode216 and first electrode 214 and the thickness of the dielectric cover294 covering the second electrode 216 are selected to coupling a desiredpower level to the effluent gas in the plasma cell 235. For example, asuitable spacing between the first and second electrodes 214, 216 may befrom about 1 mm to about 10 mm, such as about 5 mm, to couple a powerlevel of from about 50 Watts to about 5 kWatts to the treatment gas inthe plasma cell 235. A suitable thickness of the dielectric cover 294may be from about 0.5 mm to about 10 mm, such as about 3 mm. Thedielectric cover 294 may comprise a suitable dielectric material, suchas a ceramic or polymer, such as for example one or more of Teflon™ afluoropolymer available from DuPont de Nemours, Wilmington, Del.;aluminum oxide, aluminum nitride, yttrium oxide, doped ceramics,aluminum carbide, silicon carbide, silicon dioxide and compositematerial

The reactor 250 can further comprise a pre-scrubbing cell 231 havingimproved treatment gas inlets 223 that are adapted to improve thescrubbing and abatement efficiency of the reactor 250. For example, thepre-scrubbing cell 231 can form an annular sidewall 265 defining anouter circle, and treatment gas nozzles are spaced along the outercircle that are adapted to inject the treatment gas into thepre-scrubbing cell 231 at directions that are tangential to the outercircle. The nozzles can inject the treatment gas into the pre-scrubbingchamber 231 such that the treatment gas is directed against the insidesurface 221 of the annular wall 265 in the annular pre-scrubbing cell231, thereby forming an effluent gas flow path having a circularcomponent defined by the curved annular sidewall 265. The tangentiallydirected effluent may even form an effluent flow path in thepre-scrubbing chamber 231 that is substantially circular. By directingthe effluent tangentially into the pre-scrubbing cell 231, the residencetime of the treatment gas in the pre-scrubbing cell 231, and even in theplasma cell 235 is increased, thereby allowing for enhanced scrubbingand plasma abatement of the effluent. The pre-scrubbing cell 231 mayhave a size and shape that is suitable to provide a good flow oftreatment gas. For the example, the pre-scrubbing cell 231 may define across-section having a trapezoidal shape or a triangular shape.

The fluid film inlet 220 adapted to form a fluid film over surfaces inthe reactor 250 can also be positioned in the pre-scrubbing cell 231.Locating the fluid film inlet 220 in the pre-scrubbing cell 231 allowsfor the fluid film to scrub the treatment gas in the pre-scrubbing cell231 to remove undesirable materials before the treatment gas isintroduced into the plasma cell 235, as well as to add reactiveadditives from the fluid film to the treatment gas. In one version, thefluid film inlet 220 comprises an annular slit located beneath theeffluent inlets 223 along annular sidewall 265 of the pre-scrubbing cell231. The fluid film inlet 220 may also be a series of holes that arepositioned adjacent to one another. Fluid film entering thepre-scrubbing cell 231 from the fluid film inlet 220 flows by force ofgravity over the surface 221 of the annular wall 265 of thepre-scrubbing cell and over surfaces in the plasma cell 235. In theversion shown in FIG. 8 the fluid flows from the pre-scrubbing cell 231into an interior plasma cell 235 and over the inner surface 226 of theinner tube 236 comprising the embedded first electrode 214. The annularslit allows for a more uniform fluid film to be formed over the surfaceby allowing the fluid film to be flown over a larger area of thesurface. The fluid film inlet 220 may even be adapted to direct thefluid into the pre-scrubbing cell 231 in a fluid flow path having acircular component to form a rotating fluid film, thereby improving theuniform coverage of the fluid film on the surfaces in the pre-scrubbingcell and plasma cell 235.

Improved scrubbing fluid inlets 232 can also be provided to enhancescrubbing of the treatment gas in the pre-scrubbing cell 231. Thescrubbing fluid inlets 232 comprise nozzles 233 that are adapted tospray scrubbing fluid across the treatment gas flow path. Spraying thescrubbing fluid across the treatment gas flow path improves mixingbetween the treatment gas and scrubbing fluid and thereby providesbetter scrubbing of the treatment gas. In one version, the scrubbingfluid inlets 232 comprises nozzles 233 that are adapted to spray thescrubbing fluid in a direction that is substantially perpendicularrelative to the circular component of the treatment gas flow path. Forexample, the scrubbing fluid nozzles 233 can direct the scrubbing fluiddownward across the circular component of the treatment gas flow path.The scrubbing fluid can be introduced into the pre-scrubbing cell 231 bya scrubbing fluid distributor 270 comprising a manifold having aplurality of spaced apart inlets 232 above the treatment gas inlets 223,the scrubbing fluid inlets 232 being adapted to spray the scrubbingfluid in front of the treatment gas inlets 223 and across the effluentflow path as the treatment gas is introduced tangentially into thepre-scrubbing cell 231.

In one version, the scrubbing fluid nozzles 233 are adapted to direct aspray of scrubbing fluid away from a second electrode 216 having adielectric cover 294 that extends into the plasma chamber 235 andtowards, for example, the annular wall 265. Directing the scrubbingfluid away from the second electrode 216 may reduce the occurrence ofelectrical arcing between the first and second electrodes 214,216 bymaintaining the surface 217 of the embedded second electrode 216relatively dry. The spray of scrubbing fluid can be directed away fromthe second electrode 216 by angling the scrubbing fluid injector nozzles233 towards the annular sidewall 265 and away from the second electrode216. Furthermore, the spray angle of the fluid nozzles 233 can also beselected to be sufficiently narrow to avoid spraying the secondelectrode 216, while still providing a spray of scrubbing fluid that issufficiently wide to interact with and scrub the treatment gas. Forexample, a suitable spray angle may be from about 45° to about 150°,such as about 80°, for a reactor 250 having a distance between thecovered second electrode 216 and the scrubbing fluid nozzles 233 ofabout 10 cm. While the scrubbing fluid nozzles 233 have been describedas being located in the pre-scrubbing cell 231, they may also oralternatively be used in a post-scrubbing cell 229 or any other regionin the reactor 250 where a directed flow of scrubbing fluid is desired.

The scrubbing fluid inlets 232 in the pre-scrubbing cell orpost-scrubbing cells 229,231 can also comprise fluid injector nozzles233 adapted to direct the scrubbing fluid at a high velocity against afluid impingement surface, such as a surface of a wall in scrubbing orplasma cell 230, 235. The scrubbing fluid nozzles 233 can be adapted todirect the scrubbing fluid against the fluid impingement surface at avelocity that is sufficiently high to generate a scrubbing fluid mist toscrub the treatment gas. The scrubbing fluid mist is generated becausethe high impact velocity causes the impinging scrubbing fluid dropletsto break apart into smaller droplets. The smaller scrubbing fluiddroplets have a higher ratio of droplet surface area per volume ofscrubbing fluid, and thus allow for better contact with the treatmentgas and a higher scrubbing efficiency.

As described above, the corrosive effect of the reduction products suchas HF is substantially diminished at the lower operating temperatures ofthe disclosed processes. One consequence is that HF-resistant materialssuch as fluorinated polymers (e.g., Teflon® perfluorinated polyethylenesor polyvinylidene fluoride) can be used for parts of the plasma reactoror to coat exposed surfaces of the plasma reactor. Such materials tendto be less expensive than the specialized corrosion-resistant metalalloys required in harsher environments resulting from highertemperatures.

The plasma reactor may be connected to the various gas and liquidsources and exhaust gas treatment modules by any means. FIG. 5 depictsone example of a system that includes a silent-discharge, film reactor.It will be appreciated that there may be alternative arrangements of thevarious components of the system shown in FIG. 5. The system may alsoinclude further components such as additional gas sources or controldevices such as pumps and valves.

With specific reference to FIG. 5, there is provided a treatment gassource 120 and an optional gaseous reducing agent source 121. Thetreatment gas source 120 and the reducing agent source 121 are connectedto conduits 122 and 123, respectively. Conduits 122 and 123 optionallyconverge in a gas-mixing zone 124. The gas-mixing zone 124 (or conduits122 and 123) is connected to a silent-discharge, film-discharge reactor126 via gas conduit 125.

The reactor 126 includes at least one feed gas inlet 127 and at leastone exhaust or product gas outlet 128. The exhaust gas outlet 128 isconnected to a water-scrubbing unit 144 via gas conduit 145. The reactor126 also includes a first plate electrode 129 and a second plateelectrode 130 that are positioned in an opposing relationship. The firstelectrode 129 is operatively coupled to an AC voltage source 131 and thesecond electrode 130 is grounded (or connected to a low voltage source(not shown)). The first electrode 129 has an inner surface 132 uponwhich is disposed a first dielectric barrier 133. The second electrode130 has an inner surface 134 upon which is disposed a second dielectricbarrier 135. A liquid film 136 flows along the length of an innersurface 137 of the first dielectric barrier 133. A gap 146 is definedbetween an inner surface 147 of the liquid film 136 and an inner surface148 of the second dielectric barrier 135. The electrodes 129, 130,dielectric barriers 133, 135, and liquid film 136 may be made from thematerials described above.

The reactor 126 includes an inlet port 138 and an outlet port 139 forthe liquid. The outlet port 139 may be fluidly connected to a liquidreservoir 140. The liquid reservoir 140 is fluidly connected to theinlet port 138 via a liquid recycling loop 141. A fresh liquid source142 and a liquid purge conduit 143 are fluidly connected to the liquidrecycling loop 141. Waste water from the water-scrubbing unit 144 may berecycled back through the liquid recycling loop 141.

During operation the treatment gas (e.g. F₂/N₂) flowing through gasconduit 122 will optionally mix in the gas-mixing zone 124 with thereducing agent gas (e.g., H₂) flowing through conduit 123. The resultingfeed gas mixture from the gas-mixing zone 124 will flow through conduit125 and gas inlet 127 into gap 146 of the reactor 126. An AC voltagewill be applied to the first electrode 129 to generate a non-thermalplasma in the feed gas mixture flowing through the gap 146. The liquidfilm 136 (e.g., water) will flow down along the length of the innersurface 137 of the first dielectric barrier 133. The reduction reactionin the non-thermal plasma will occur at or near the inner surface 147 ofthe liquid film 136. The heat produced by the reduction reaction may beabsorbed by the liquid film 136. In addition, water-soluble reactionproducts (e.g., HF) may dissolve into the liquid film 136. Liquid thatincludes a sufficient concentration of dissolved reaction products maybe removed from the system via the liquid purge conduit 143. The gasexiting the reactor 126 through the exhaust gas outlet 128 may includereaction products (e.g., HF) and any non-reacted inert gases (e.g., N₂).The water-soluble reaction product(s) are then treated in thewater-scrubbing unit 144.

Control of such a system exemplified by FIG. 5 may be implemented by anyof the techniques well known in process control. For example, a sensormay be placed in an appropriate location in the system to monitor therelevant parameters of the treatment gas, particularly the halogenconcentration. Data from this sensor may be inputted into a computercontroller that determines the appropriate responsive settings for otheroperating parameters of the system (e.g., reducing agent concentration,voltage to the plasma reactor electrode, water flow rate, etc.). Thecontroller then generates instruction signals to the control devices foreach such operating parameter.

One such sensor could be placed at the treatment gas inlet into thechamber for measuring the halogen concentration and adjusting the amountof reducing agent and liquid flow rate accordingly. For example, in thesystem of FIG. 5 a sensor for detecting halogen concentration may beoperatively coupled to gas conduits 122, 123 and/or 125 and to liquidrecycling loop 141. Another useful parameter for monitoring may be thevoltage and current measured from the high voltage electrode to theground electrode. For example, in the system of FIG. 5 a voltage probemay be operatively coupled to the first electrode 129 and a sensingcapacitor may be operatively coupled to the second electrode 130. Amethod for obtaining the plasma power input with such aprobe-and-capacitor arrangement is described in Rosenthal, L. and Davis,D., “Corona Discharge for Surface Treatment”, IEEE Transactions ofIndustry Applications, I-5, 328 (May/June 1975).

As mentioned above, the disclosed process is especially suitable fortreatment of effluent streams from semiconductor manufacturing processessuch as plasma etch, plasma-enhanced chemical vapor deposition andplasma-assisted chamber cleaning processes. In such manufacturingprocesses there is often a dry or roughing pump or similar devicelocated downstream of the etch or deposition process tool that dilutesthe effluent with an inert gas such as nitrogen. According to oneembodiment of the disclosed process, the plasma reactor for carrying outthe process is located downstream from such an inert gas source and,thus, N₂ (or other inert gas) constitutes a substantial portion of thetreatment feed gas mixture. In other words, this specific embodiment isnot a so-called “point-of use” abatement system since it is not treatingthe effluent stream immediately after it exists the etch or depositionchamber.

The specific examples described below are for illustrative purposes andshould not be considered as limiting the scope of this disclosure.

EXAMPLE 1

A treatment gas containing 1000 ppm F₂ in N₂ background gas was mixedwith various H₂ streams (at a 1:1 H₂:F₂ molar ratio and a 2:1 H₂:F₂molar ratio). The treatment gas and H₂ were supplied at ambienttemperature and pressure. The resulting feed gas mixtures wereintroduced into the annular gap of a silent discharge plasma reactorhaving a configuration as shown in FIG. 4. A non-thermal plasma wasgenerated in the feed gas mixtures with AC voltages having differentfrequencies applied to the high voltage electrode (400 Hz, 200 Hz and100 Hz). The reactor temperature ranged from 30-35° C. The resultingamount of F₂ in the exhaust gas stream and energy required is shown inthe graph of FIG. 6.

EXAMPLE 2

Treatment gases containing 4000, 2000, or 1000 ppm F₂ in N₂ backgroundgas were mixed an H₂ stream at a 2:1 H₂:F₂ molar ratio. The treatmentgas and H₂ were supplied at ambient temperature and pressure. Theresulting feed gas mixtures were introduced into the annular gap of asilent discharge plasma reactor having a configuration as shown in FIG.4. A non-thermal plasma was generated in the feed gas mixtures with a200 Hz AC voltage applied to the high voltage electrode. The reactortemperature ranged from 30-35° C. The resulting amount of F₂ in theexhaust gas stream and energy required is shown in the graph of FIG. 7.

Having illustrated and described the principles of our disclosure withreference to several embodiments, it should be apparent to those ofordinary skill in the art that the invention may be modified inarrangement and detail without departing from such principles.

1. A process for treating a halogen-containing gas, comprising:introducing a halogen-containing gas into a reactor; introducing aliquid reducing agent into the reactor; vaporizing a portion of theliquid reducing agent in the reactor; generating a non-thermal plasma inthe reactor in the presence of a non-vaporized portion of the liquidreducing agent to reduce the halogen-containing gas; and removing theresulting reduction product from the reactor, wherein the non-vaporizedportion of the liquid reducing agent forms a liquid region with a liquidsurface facing an interior of the reactor.
 2. The process according toclaim 1, wherein the non-vaporized portion of the liquid reducing agentflows through the reactor during generation of the non-thermal plasma.3. The process according to claim 1, wherein the liquid reducing agentis selected from water, a high vapor pressure hydrocarbon, an olefin, ora reducing agent dissolved in a liquid carrier.
 4. The process accordingto claim 3, wherein the liquid reducing agent comprises water.
 5. Theprocess according to claim 1, wherein the vaporizing of a portion of theliquid reducing agent is effected by the liquid reducing agent absorbingheat produced by the reduction of the halogen-containing gas.
 6. Theprocess according to claim 1, wherein the non-thermal plasma comprises asilent discharge plasma.
 7. The process according to claim 2, whereinthe resulting reduction product comprises at least one water-solublehalogen-containing substance, and the removing of the resultingreduction product from the reactor comprises dissolving thewater-soluble halogen-containing substance in the non-vaporized portionof the liquid reducing agent and discharging the resulting solution fromthe reactor.
 8. A continuous process for treating a halogen-containinggas, comprising: providing a reactor defining at least one gas inlet forreceiving a halogen-containing gas, and at least one inlet for receivinga liquid reducing agent; providing at least one first electrode and atleast one second electrode disposed within the reactor; flowing theliquid reducing agent over at least a portion of the first electrode;vaporizing a portion of the liquid reducing agent in the reactor; andapplying electric potential to at least one of the first electrode orthe second electrode so as to generate a plasma that reduces thehalogen-containing gas in the continuous presence of a non-vaporizedportion of the liquid reducing agent.
 9. The process according to claim8, wherein a dielectric barrier is disposed on a surface of the firstelectrode, and the generated plasma comprises a non-thermal plasma. 10.The process according to claim 8, wherein the liquid reducing agent isselected from water, a high vapor pressure hydrocarbon, an olefin, or areducing agent dissolved in a liquid carrier.
 11. The process accordingto claim 8, wherein reducing the halogen-containing gas produces areaction product mixture that includes a water-solublehalogen-containing reduction product, the process further comprisingseparating the water-soluble halogen-containing reduction product fromthe reaction product mixture.
 12. The process according to claim 11,wherein the separating comprises aqueous scrubbing.
 13. The processaccording to claim 11, the process further comprising dissolving thewater-soluble halogen-containing reduction product into the liquidreducing agent.
 14. The process according to claim 13, furthercomprising adding at least calcium hydroxide or sodium hydroxide to theliquid reducing agent.
 15. The process according to claim 7, furthercomprising adding at least calcium hydroxide or sodium hydroxide to theliquid reducing agent.
 16. A process for treating F₂ gas, comprising:introducing F₂ gas into a chamber; introducing a liquid reducing agentinto the chamber; vaporizing a portion of the liquid reducing agent inthe chamber; generating a non-thermal plasma in the chamber in thepresence of a non-vaporized portion of the liquid reducing agent toreduce the F₂ gas into hydrogen fluoride; and removing the resultinghydrogen fluoride from the chamber, wherein the non-vaporized portion ofthe liquid reducing agent forms a liquid region with a liquid surfacefacing an interior of the chamber.
 17. The process according to claim16, wherein the non-vaporized portion of the liquid reducing agent flowsthrough the chamber during generation of the non-thermal plasma.
 18. Theprocess according to claim 16, wherein the liquid reducing agent isselected from water, a high vapor pressure hydrocarbon, an olefin, or areducing agent dissolved in a liquid carrier.
 19. The process accordingto claim 18, wherein the liquid reducing agent is water.
 20. The processaccording to claim 16, wherein the vaporizing of a portion of the liquidreducing agent is effected by the liquid reducing agent absorbing heatproduced by the reduction of the F₂ gas.
 21. The process according toclaim 1, wherein the non-thermal plasma is generated at a temperatureless than or equal to about 100° C.
 22. The process according to claim1, wherein the liquid region is contiguous with an inner surface of thereactor.